It is well-known in the art for the manufacture of disposable baby diapers or other sanitary disposable absorbent products such as sanitary napkins, adult incontinence pads, and hospital bed pads to provide a structure wherein the coversheet or coverstock or top sheet (i.e., that portion of the product which is in contact with the patient's skin) is made of hydrophyllic material so as to be pervious, to liquids such as urine. This permits ready pass-through of the liquid into the absorbent core or the pad which lies beneath the coverstock. In the past, some of the coverstocks have also been made of cotton, or blends of cotton and rayon or blends of rayon with a bonding fiber such as polyethylene.
Such coverstock, however, has been undesirable because it tends to retain the moisture and thus feel wet to touch and because it keeps the skin wet and is more likely to cause skin rash or diaper rash or the like.
Therefore, in more recent years, it has been found desirable to use a coverstock made of hydrophobic fibers or filaments, such as polypropylene or polyester, either carded, spun-bonded or melt-blown, or the like, but because such material inherently tends to interfere with the pass-through of urine into the absorbent pad, it has been found necessary to treat the web with a hydrophyllicity-inducing material (surf actant) such as Triton X-102 distributed by Rohm & Haas Co. of Philadelphia, Pa. or MAGNASOFT manufactured by the Union Carbide Company.
The surfactant usually is incorporated with the fibers by the fiber manufacturers before being sent to the web manufacturer, who form a web which is substantially uniformly hydrophyllic. A web thus formed when used as the top sheet in a baby or adult diaper is then coated in areas where perviousness is not only unnecessary but also undesirable. In a more recent form of diaper construction, a strip of nonwoven web of hydrophyllic material is assembled side-by-side between two strips or webs of hydrophobic fibers. When such a 3-strip web is placed upon a diaper, with the pervious strip in the longitudinal center of the diaper, the urine can pass to the absorbent core through the center strip but not along the sides where the coverstock is impervious. However, such a pre-formed, web assembled from three different materials is costly to make and more difficult to run on a diaper machine because of the seam-lines between the hydrophyllic and hydrophobic strips.
In order to overcome such deficiencies, this invention provides a process for applying a coating material to a one-piece hydrophobic web only where the coating is desired.
Such a process is different from a padding process which applies a liquid, such as an adhesive, to an unbonded web of fibers (to create an integrated nonwoven web).
The prior art fails to teach the unique process of the present invention to produce a one-piece web with precisely-located coating zones.